This invention relates to the control of drivetrain retarders of vehicles. Drivetrain retarders are devices that can be operated to absorb power from a drivetrain of a vehicle in motion in order to reduce the vehicle""s speed. There are a number of types of drivetrain retarders that are well known. Engine compression brakes and exhaust brakes are well known types of drivetrain retarders. In vehicles driven by electric motors it is well known to utilize the vehicle""s electric drive motor as a drivetrain retarder by causing it to operate as an electrical generator. Drivetrain retarders in the form of hydraulic pumps and other similar devices that can be coupled to the vehicle""s drivetrain in order to absorb power are also well known.
Control of such drivetrain retarders includes controlling whether the drivetrain retarder""s operational state is on or off and controlling the resistance level of the drivetrain retarder. When a vehicle is in motion and such control systems of the vehicle cause a drivetrain retarder of the vehicle to be in an on operational state the drivetrain retarder absorbs power from the vehicles drivetrain and, thus, retards the motion of the vehicle. When such control systems of a vehicle cause a drivetrain retarder to be in an off operational state the drivetrain retarder absorbs substantially no power from the drivetrain of the vehicle and, thus, does not retard motion of the vehicle. Many drivetrain retarders are constructed so that they can be selectively operated at one of a plurality of resistance levels. All other conditions being the same, such a drivetrain retarder absorbs different amounts of power when it is operated at each of its different resistance levels. For example, many engine compression brakes activate compression braking of a different number of engine cylinders when the engine compression brake is operated at each different one of its resistance levels.
Known control systems of drivetrain retarders accommodate only relatively simplistic methods for controlling the operational state and the resistance levels of such drivetrain retarders. Many retarder control systems control the operational state and the resistance level of a drivetrain retarder dependent only upon the operational states of a retarder state selector and a retarder resistance selector which are manually controlled by an operator of the vehicle. For example, many retarder control systems for engine compression brakes of vehicles control the operational state and the resistance level of the engine compression brake based entirely upon the operational state of an on/off switch and a resistance level switch that are both manually controlled by a vehicle operator. Examples of retarder control systems that control the operational state of a drivetrain retarder based upon factors other than the operational state of a retarder state selector are known. It is known to construct a retarder control system in such a manner that, when an Anti-Lock Braking system of the vehicle is actived, the operational state of the drivetrain retarder is caused to become off regardless of the operational state of the retarder state selector of the retarder control system. It is not known to construct retarder control systems that control the resistance level of a drivetrain retarder based upon factors other than the operational state of a retarder resistance selector. Therefore, when a drivetrain retarder is caused by its retarder control system to be in an on operational state, the drivetrain retarder will operate at whatever resistance level is effected by the operational state of the retarder resistance selector of the retarder control system. In many cases operation of the drivetrain retarder at the resistance level effected by the operational state of the retarder resistance selector is not ideal.
As a result, an object of the present invention is to provide a method of operation of a retarder control system that controls the resistance level at which a drivetrain retarder is operated based upon factors other than the operational state of a retarder resistance selector. A further object of the invention is to provide a retarder control system that can be operated according to a method in which the resistance level at which a drivetrain retarder is operated is controlled based upon factors other than the operational state of a retarder resistance level selector.
The present invention is a method of operation of a retarder control system that controls the resistance level at which a drivetrain retarder is operated based upon one or more of a number of factors other than the operational state of a retarder resistance selector. The resistance level that the drivetrain retarder is caused to operate at by the retarder control system may depend upon one or more factors such as rotational speeds of various components of the drivetrain of the vehicle, vehicle speed, rotational speeds of undriven wheels of the vehicle, brake pedal position, elapsed time after brake pedal actuation, and elapsed time after initiation of operation of the drivetrain retarder in the on operational state. The retarder control system of the present invention includes any devices such as sensors, timers, switches, and computing devices necessary to enable it to control the resistance level of the drivetrain retarder according to one or more of the above mentioned factors. The present invention also includes a vehicle that has a drivetrain retarder and a retarder control system that operate according to the method of the present invention. The present invention also includes a computer program for causing the retarder control system of the present invention to operate according to the method of the present invention.